Many electronic devices communicate with other devices using ethernet cables and ethernet standards or protocols. For example, clients and hosts may communicate with each other by way of an ethernet cable. An ethernet cable has four pairs of cables for a total of eight conductors. In some ethernet standards, only two of the four pairs are used for data transmissions. In more recent standards, all four pairs are used for data transmissions.
Electronic devices used for communications need to be powered and they need to transmit and receive data, which requires the electronic devices to be connected to both the ethernet cable and a power cable. In order to reduce the cabling and allow the electronic devices to be located away from power sources, power has been transmitted to the electronic devices by way of the ethernet cable. For example, a remote camera may be connected to an ethernet cable that provides for power to be transmitted to the camera and data to be transmitted to and from the camera. Thus, the location of the remote camera is not dependent on the location of a power source. Sending data and power over an ethernet cable is referred to as power over ethernet or PoE. The device supplying power is referred to as the PSE or power source equipment and the device being powered is referred to as the PD or the powered device.
Many of the ethernet standards include standards for PoE. In some standards only two of the four pairs of conductors are used for data transmissions. In these standards, one mode uses the same two pairs of conductors for data and power transmission. Another standard uses the two pairs of conductors that are not used for data transmissions to transmit power. A newer ethernet standard uses all four pairs of conductors for data transmission and two pairs for power transmission. These standards limit the amount of power that can be transmitted to a device using PoE.
Some of the standards require some sort of communication between the PSE and the PD. For example, the PSE may send data to the PD indicating the amount of power that it can source. The PD may also send data indicating that it is the type of device that can be powered. The data communications are time consuming and require additional hardware and software in the PSE and the PD, which increases their costs.